A geometric method for isomorphically transforming the shape of biological structures expressed as two dimensional projections is being applied to cephalograms and anatomical specimens to determine constraints underlying growth and development. The rationale underlying this effort is based on the assumption that the relatively small amount of systematic progress in quantitative morphology may be attributed to a lack of coordinate independent bases for mathematical description. Symmetric-axis geometry permits angular relationships between symmetrically determined branches to be quantitatively assessed by superposition of homologous elements. When this method is applied to lateral projections of the human mandible, branch angles determined by the condyle, coronoid, and upper ramus have been shown to be relatively independent of age within and between individuals. Recent measurements on certain primates and various strains of mice confirm that this homologous angular invariance is not limited to humans, but that the angles can vary with species.